This invention relates to a method of making .alpha.,.alpha.,.alpha.,-trifluoromethoxybenzene by reacting an .alpha.,.alpha.,.alpha.,-trichloromethoxybenzene or an .alpha.,.alpha.,.alpha.,-tribromomethoxybenzene with hydrogen fluoride. In particular, it relates to performing this reaction using gaseous hydrogen fluoride at atmospheric pressure.
.alpha.,.alpha.,.alpha.,-Trifluoromethoxybenzene is an intermediate used in making agricultural chemicals. It has been made by a variety of different processes, including the reaction of hydrogen fluoride with .alpha.,.alpha.,.alpha.,-trichloromethoxybenzene. That reaction has been performed using liquid hydrofluoric acid at low temperatures and gaseous hydrofluoric acid at high temperatures and high pressures, with and without catalysts, usually with a large excess of hydrogen fluoride. The reaction is difficult to perform under these conditions because hydrogen fluoride is such a highly reactive and dangerous chemical. In addition to the safety problems, the yields are often low, and the product is frequently contaminated with byproducts and tar.